Brake equipment in the vehicle brake field generally comprises a service brake system and a parking brake system.
It is also usual to provide each vehicle wheel with a brake having a disc- or drum-shaped friction surface as well as a friction element and an actuator, which presses the friction element against the friction surface when the brake is operated. The subassembly comprising the actuator and the friction element is called xe2x80x9cactuator subassemblyxe2x80x9d in the following.
In a motor vehicle the service and the parking brake system generally employ a common brake, whereas their operating and transmission devices are separate. This is required for safety reasons and on account of legal regulations.
In this respect the operation of the actuator subassembly for a service brake function is usually effected by the pedal force and an auxiliary force, with pneumatic (vacuum, compressed air), hydraulic and also electrical energy primarily being used to produce the auxiliary force. In contrast, the parking brake system is generally operated manually, by hand or foot, and maintained in this state by mechanical means.
The object of more recent developments of vehicle brakes is also to perform the parking brake function by means of auxiliary energy, such as, e.g. electrical energy, in order to simplify the brake system. A further aim is to minimise the constructional volume and the weight of the brake at the wheel in order to keep the unsprung mass of the motor vehicle as low as possible.
Where known vehicle brakes are concerned, the holding force for a parking brake function is applied by means of auxiliary or external energy directly by a drive of the actuator subassembly. In this connection locking and emergency release devices are required in case the power supply for the drive, e.g. the electricity supply of an electric motor, should fail, so that the parking brake initially remains locked and can be released if required. Devices of this kind are expensive and in some cases require a considerable amount of power for the drive.
The applicant""s publication WO 98/01682 discloses an actuator subassembly in which a drive can move a friction element of the vehicle brake via a toggle arrangement. This actuator subassembly can also perform the function of a parking brake by introducing an additional input force into the toggle arrangement. However the fact that a permanent, very high holding force has to be applied while operating the parking brake proves to be problematic in this respect.
The object of the invention is therefore to provide an actuator subassembly module for a vehicle brake which does not have these disadvantages. This object is achieved by the actuator subassembly indicated in Claim 1. Subclaims relate to advantageous developments. Further features, advantages and properties of the invention are illustrated on the basis of the following description with reference to the drawings.